Render region and render with 1 keystroke?
I took p2or link and modified a little. After running the script, shortcut key is Shift + Q.
def register() part has type = "Q" and shift = True alt = False and ctrl = False.

bl_info = {
    "name": "Toggle Simplify",
    "description": "Toggle Simplify",
    "author": "poor",
    "version": (0, 0, 2),
    "blender": (2, 79, 6),
    "location": "3D View",
    "category": "3D View"
}

import bpy


# operator
class ToggleSimplify(bpy.types.Operator):
    """Tooltip"""
    bl_idname = "view3d.toggle_simplify"
    bl_label = "Toggle Simplify"
    bl_options = {'REGISTER'}

    border = bpy.props.BoolProperty(default=False)

    def execute(self, context):

        if bpy.context.area.spaces.active.use_render_border:
            bpy.context.area.spaces.active.use_render_border = False
            self.border = False
            bpy.ops.view3d.toggle_render()
        else:
            bpy.ops.view3d.render_border("INVOKE_DEFAULT")

        context.window_manager.modal_handler_add(self)
        return {'RUNNING_MODAL'}

    def modal(self, context, event):

        if not self.border and context.area.spaces.active.use_render_border:
            bpy.ops.view3d.toggle_render()
            self.border = True
            return {'FINISHED'}
        return {'PASS_THROUGH'}


addon_keymaps = []


# register
def register():
    bpy.utils.register_class(ToggleSimplify)

    # handle the keymap
    wm = bpy.context.window_manager
    kc = wm.keyconfigs.addon
    if kc:
        km = wm.keyconfigs.addon.keymaps.new(name='3D View', space_type='VIEW_3D')
        kmi = km.keymap_items.new(ToggleSimplify.bl_idname, type='Q', value='PRESS', shift=True, alt=False, ctrl=False)
        addon_keymaps.append((km, kmi))


# unregister
def unregister():
    for km, kmi in addon_keymaps:
        km.keymap_items.remove(kmi)
    addon_keymaps.clear()

    bpy.utils.unregister_class(ToggleSimplify)


if __name__ == "__main__":
    register()